The flag is a Canadian pale, yellow-green-yellow, with a shield centred, "Or on a Canadian pale Vert
an escutcheon of the Arms."

The colour yellow represents Saint-Malachie’s primary industry, agriculture (poultry, dairy and pork products). The two croziers symbolize the fact that St. Malachy (1094-1148), patron of the municipality, was Archbishop of Armagh, Ireland. The toad is derived from the municipality’s history, referring to the toad (crapaud in French) infestation of 1873. This event also gave rise to the name La Crapaudière, the mountain in the area. The shamrocks symbolize the Irish roots of Saint-Malachie’s pioneers.
Source:
http://reg.gg.ca/heraldry/pub-reg/project.asp?lang=e&ProjectID=1051&ShowAll=1